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1.
(001)YBa2Cu3O7−δ epitaxial films were prepared by laser ablation on surface. A thin (001)CeO2 or (111)CeO2 buffer layer was deposited between the substrate and the superconductor film to reduce their chemical interaction. In the initial stages of CeO2 buffer formation, its orientation depended strongly on the intensity of cerium ion interaction with oxygen. Epitaxial growth of (001)YBa2Cu3O7−δ films was achieved both on and . The T c temperature of epitaxial (001)YBa2Cu3O7−δ films was within 88–90 K, and the current J c at 77 K was in excess of 106 A/cm−2. Fiz. Tverd. Tela (St. Petersburg) 40, 205–208 (February 1998)  相似文献   

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EPR and the method of dielectric losses have been used to investigate Fe3+ centers of axial and orthorhombic symmetry in KTaO3 single crystals. The EPR spectrum of orthorhombic-symmetry Fe3+ obtained in the 8-mm wavelength range at T=77 K is described by the spin-Hamiltonian with parameters g x=1.98, g y=2.01, g z=2.00, D=0.43 cm−1, and E=5.87×10t-2 cm−1. From the dielectric measurement data we have obtained the following parameters of the relaxation of the orthorhombic Fe3+ centers in KTaO3: characteristic relaxation frequency τ 0 −1 =2.33×1012 Hz and activation energy E a=0.044 eV. A model of the orthorhombic Fe3+ center in KTaO3 is discussed within the framework of the kinetic parameters obtained. Fiz. Tverd. Tela (St. Petersburg) 39, 861–864 (May 1997)  相似文献   

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(NH4)3VO2F4 crystals were grown, and polarization-optical studies and measurements of birefringence were conducted on crystal plates of various cuts over a wide temperature range. Phase transitions were detected at temperatures T 1↑ = 417 K, T 3↑ = 211 K, and T 4↑ = 205 K (on heating) and at T 1↓ = 413 K, T 3↓ = 210 K, and T 4↓ = 200 K (on cooling). The transitions are accompanied by anomalies of the birefringence and by twinning. The sequence of changes in the phase symmetry is assumed to be as follows: cubic Fm m ↔ orthorhombic Immm (I2221) ↔ monoclinic 112/m) ↔ triclinic P . Near temperatures T 2 ≈ 240–250 K, an additional anomaly of the birefringence is observed, with the crystal retaining the orthorhombic symmetry. Original Russian Text ? S.V. Mel’nikova, A G. Kocharova, 2009, published in Fizika Tverdogo Tela, 2009, Vol. 51, No. 3, pp. 562–564.  相似文献   

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A method for determining the angle γ and the ratio of the amplitudes A λ(B K *−) and A λ)B D *0 K *−), r , for all three vector-meson polarization states by using the decays B D * K *∓ is proposed. This method relies on the interference between the decays B D *0 K *− and B K *−, which arises if D *0 and decay to D 0/ π 0 and D 0/ γ, whereupon D 0 and mesons decay to common final hadron states. The doubly Cabibbo-suppressed modes of D 0-meson decay are chosen here to specify such final states. Original Russian Text ? V.A. Kovalchuk, 2007, published in Yadernaya Fizika, 2007, Vol. 70, No. 4, pp. 754–763.  相似文献   

7.
The colossal negative magnetoresistance Δρ observed in La0.6Y0.1Ca0.3MnO3 at B=1 T shows an unusual, nearly perfect symmetry (around the peak temperature T 0=160 K), suggestive of a Curie-Weiss-dominated transport mechanism in this material both above and below the field-dependent Curie temperature T CT 0. Attributing this symmetry to strong magnetic fluctuations below T C (which are triggered by the Y substitution and cause a “bootstrap” destruction of the ferromagnetic phase), the data are interpreted in terms of the nonthermal spin hopping and magnetization-dependent charge carrier localization scenario leading to , with the magnetization M(T,B)=CB/|T−T C(B)|ν. The separate fits through all the data points above and below T C yield C +≃2C and ν+≃ν≃1, in agreement with the predictions of the Landau mean-field theory. Pis’ma Zh. éksp. Teor. Fiz. 70, No. 2, 136–140 (25 July 1999) Published in English in the original Russian journal. Edited by Steve Torstveit.  相似文献   

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The temperature dependences of the heat capacity, the unit cell parameter, and the permittivity for the (NH4)3MoO3F3 cryolite (space group Fm $ \overline 3 The temperature dependences of the heat capacity, the unit cell parameter, and the permittivity for the (NH4)3MoO3F3 cryolite (space group Fm m) are investigated. It is revealed that the compound undergoes ferroelectric and ferroelastic structural phase transitions at temperatures of 297 and 205 K, respectively. The mechanism of structural distortions is discussed in terms of the entropy parameters, pressure-temperature phase diagrams, and electron density maps for critical atoms. An analysis is made of the influence of the cation size and shape on the phase transitions in oxyfluorides of the general formula A 2 AMO3 (A,A′ = NH4, K; M = Mo, W). Original Russian Text ? I.N. Flerov, V.D. Fokina, A.F. Bovina, E.V. Bogdanov, M.S. Molokeev, A.G. Kocharova, E.I. Pogorel’tsev, N.M. Laptash, 2008, published in Fizika Tverdogo Tela, 2008, Vol. 50, No. 3, pp. 497–506.  相似文献   

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Dirac’s large number hypothesis (LNH), in the formG/G 0=HH 0 −1 , is applied to the matter-dominated cosmological era, using the framework of the scale covariant theory (Canuto et al., 1977). We obtain explicit expressions forR andβ a as functions ofR E , whereR andR E are the scale factors of the cosmological Robertson-Walker metric, expressed in atomic and gravitational units, respectively, andβ a is the ratio between the rates of gravitational and atomic clocks. The parameters in these expressions are , the deceleration parameter in gravitational units, and (t 0)H 0 −1 where (t 0) is the present epoch value of the derivative ofβ a with respect to atomic time. We find that a necessary condition for the LNH to be compatible with a Robertson-Walker model is that (t 0)H 0 −12 1 . The only experimental values for (t 0) available at present are those based on the lengthening of the Moon’s period of revolution around the Earth, suggesting 0.86≥ (t 0)H 0 −1 ≥0.21; the more promising technique of radar ranging to the inner planets has not yet produced a value for (t 0). Using the lunar data, it follows that 0≤ ≲0.42 corresponding to an open universe (k=−1). Closed models (k=1, >1/2) are not compatible with the LNH since the required values of (t 0)H 0 −1 are more than an order of magnitude above the observational upper limit. Presented at the Dirac Symposium, Loyola University, New Orleans, 1981.  相似文献   

11.
In the framework of the spectral integral equation, we consider the states and their radiative transitions. We reconstruct the interaction on the basis of data for the levels of the bottomonium states with J PC = 0−+, 1−−, 0++, 1++, 2++ as well as the data for the radiative transitions γ (3S) → γχbJ(2P) and γ(2S) → γχbJ(1P) with J = 0, 1, 2. We calculate bottomonium levels with the radial quantum numbers n ≤ 6, their wave functions, and corresponding radiative transitions. The ratios Br[χbJ(2P) → γγ(2S)]/Br[χbJ(2P) → γγ(1S)] for J = 0, 1, 2 are found to be in agreement with data. We determine the component of the photon wave function using the data for the e + e annihilation, e + e → γ(9460), γ(10 023), γ(10 036), γ(10 580), γ(10 865), γ(11 019), and predict partial widths of the two-photon decays ηb0 → γγ, χb0 → γγ, χb2 → γγ for the radial excitation states below the threshold (n ≤ 3). The text was submitted by the authors in English.  相似文献   

12.
The relaxation timesT 1,T 1q,T 1D, andT 2 for1H in the tetragonal-A phase of HxWO3 have been measured over the temperature range 190 to 490 K. The1H relaxation behaviour appears to be governed by diffusion over inequivalent jump distances, approximating to a short range planar diffusion and a long range isotropic diffusion. Parameters for the latter motion are estimated asE a = 68 kJ/mol and 0=2.5×10–13 s. The powder X-ray diffraction pattern for this phase of HxWO3 has been studied over the temperature range 300–470 K. The tetragonal distortion diminishes with temperature and H0.43 WO3 becomes cubic at about 435 K. Volumetric studies of hydrogen evolution show that decomposition accelerates at approximately this temperature.  相似文献   

13.
The mechanism of dipion transitions nSn′Sππ (n = 3, 2; n′ = 2, 1) in bottomonium and charmonium is studied with the use of the chiral string-breaking Lagrangian allowing for the emission of any number of π(K, ν), and not containing fitting parameters. The transition amplitude contains two terms: M = a − b, where the first term (a) refers to subsequent one-pion emission, , and the second term (b) refers to two-pion emission, . The one parameter formula for the dipion mass distribution is derived, dw/dq∼ (phase space) × | ηx|2, where x = (q 2 − 4m π2)/(q max2 − 4m π2), q 2 m= M ππ2. The parameter ν dependent on the process is calculated, using SHO wave functions and imposing PCAC restrictions (Adler zero) on amplitudes a and b. The resulting dipion mass distributions are in agreement with experimental data. The text was submitted by the authors in English.  相似文献   

14.
The LHC (CMS) discovery potential in the search for supersymmetry and lepton-flavor violation in neutralino decays using the e ± μ + E T miss signature is studied. A detailed study is done for the CMS test points LM1-LM9. It is shown that, for the point LM1, it is possible to detect lepton-flavor violation in neutralino decays with lepton-flavor-violating branching Br( → μ± e ) ≥ 0.04 Br( → e + e , μ+ μ ) for an integral luminosity of 10 fb−1. The discovery potential in the mSUGRA-SUSY scenario with tan β = 10, sgn(μ) = + in the (m 0, m 1/2) plane using the e ± μ + E T miss signature is determined. The text was submitted by the authors in English.  相似文献   

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a     
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16.
The signs of the experimental values of the multipole-mixture parameters δ are compared with the signs of = Σa i μ i for (2+02−2+01) and (2+03−2+01) transitions and with the signs of = Σa i [(μ i + μ ) or (μ − 1/2)] for (2+21−2+01) transitions in nonspherical even-even nuclei, where a i is the contribution of the ith pair of quasiparticles to the wave function for 2+02, 2+03, and 2+21 single-phonon states according to the quasiparticle-phonon model and μ is the magnetic moment for the corresponding Nilsson state. Original Russian Text ? A.M. Demidov, L.I. Govor, V.A. Kurkin, I.V. Mikhailov, 2009, published in Yadernaya Fizika, 2009, Vol. 72, No. 2, pp. 228–235.  相似文献   

17.
Ramesh C Verma  M P Khanna 《Pramana》1978,11(3):333-351
Weak decay modes (1/2+ → 3/2+ + 0/γ) of charmed baryons are studied. Relations among the various decay amplitudes are derived in isospin, SU(3), SU(4) and SU(8) w symmetries. Sextet dominance in SU(3) forbidsB(3) →D(10) +P(3*) decays. 20″ dominance in SU(4) specifies all the decays in terms of Θ decays. Weak decays of Θ* 3 ++ and Θ are also discussed. SU(8) w symmetry predictsα , which is consistent with the experimental value.  相似文献   

18.
Ceramic samples of (1−x)SrTiO3-xSrMg1/3Nb2/3O3 and (1−x)SrTiO3-xSrSc1/2Ta1/2O3 were prepared, and their dielectric properties were studied at x=0.005–0.15 and 0.01–0.1, respectively, at frequencies 10 Hz–1 MHz and at temperatures 4.2–350 K. A giant dielectric relaxation was observed in the temperature range 150–300 K, and not so strong but well-developed relaxation was found in the temperature range 20–90 K. The activation energy U and the relaxation time τ0 were determined to be 0.21–0.3 eV and from 10−11 to 10−12 s for the high-temperature relaxation and 0.01–0.02 eV and 10−8–10−10 s for the low-temperature relaxation, respectively. The additional local charge compensation of the heterovalent impurities Mg2+ and Nb5+ (or Sc3+ and Ta5+) by free charge carriers or the host ion vacancies is suggested to be the underlying physical mechanism of the relaxation phenomena. On the basis of this mechanism, the Maxwell-Wagner model and the model of reorienting dipole centers Mg2+ (or Sc3+) associated with the oxygen vacancy are proposed to explain the high-temperature relaxation with some arguments in favor of the latter model. The polaron-like model with the Nb5+-Ti3+ center is suggested as the origin of the low-temperature relaxation. The reasons for the absence of ferroelectric phase transitions in the solid solutions under study are also discussed. From Fizika Tverdogo Tela, Vol. 44, No. 11, 2002, pp. 1948–1957. Original English Text Copyright ? 2002 by Lemanov, Sotnikov, Smirnova, Weihnacht. This article was submitted by the authors in English.  相似文献   

19.
For the kernel of the Laplace operator ΔΛ with potential Σ j=1 k c j δ q j (x) on a manifold, (the operator is given by a Lagrangian plane Λ ⊂ ℂ k ⊕ ℂ k ), an isomorphism Γ: ker ΔΛ → Λ ∩ L is described, where L is a special Lagrangian plane (whose explicit form is evaluated). A similar assertion holds for the Laplace operator on a decorated graph; for such a graph (obtained by decorating a connected finite graph with n edges and v vertices) with “continuity” conditions, the inequality 1 ≤ dimker ≤ nv + 2 is obtained. It is also proved that the quantity nv + 1-dim ker cannot reduce when adding new edges and manifolds. The first terms of the expansion of Tr(exp(-tH Λ)) are found. Dedicated to the memory of V. A. Geyler  相似文献   

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